One type of check valve generally comprises a valve body with a bore therethrough for the flow of fluid and a flapper that moves between open and closed positions to allow or to block, respectively, fluid flow. The flapper often has an integral pin (or trunnion), which is held in a recess in the valve body, and the flapper rotates on the longitudinal axis of the pin.
Valves and blocking structures are shown in U.S. Pat. No. Re. 21,334, U.S. Pat. Nos. 326,549, 542,417, 705,255, 846,317, 891,012, 922,262, 1,325,568, 1,505,958, 1,673,831, 1,742,043, 2,089,141, 2,265,596, 2,268,806, 2,271,390, 2,342,485, 2,419,318, 2,482,198, 2,532,067, 2,657,824, 2,664,264, 2,767,735, 2,918,934, 2,930,400, 2,959,188, 3,008,650, 3,016,914, 3,023,771, 3,038,494, 3,058,534, 3,066,693, 3,128,785, 3,131,719, 3,144,876, 3,363,645, 3,370,305, 3,482,603, 3,509,908, 3,565,107, 3,604,453, 3,612,097, 3,613,720, 3,618,893, 3,705,602, 3,720,228, 3,726,341, 3,762,438, 3,770,242, 3,817,277, 3,933,173, 3,937,441, 3,974,848, 3,990,471, 4,039,004, 4,054,153, 4,061,535, 4,075,832, 4,114,202, 4,128,111, 4,194,722, 4,196,745, 4,201,241, 4,230,150, 4,274,436, 4,304,255, 4,307,747, 4,427,025, 4,433,702, 4,478,244, 4,480,812, 4,480,815, 4,484,365, 4,485,844, 4,485,846, 4,488,318, 4,488,566, 4,488,571, 4,492,249, 4,493,338, 4,494,564, 4,494,729, in French Pat. No. 2,216,496, and in U.K. Pat. No. 1,214,619.
In U.S. Pat. No. 3,565,107, the pipe flange traps the ends of the flapper pin in the flapper pin groove, thereby keeping the pin in place. In U.S. Pat. Nos. 2,930,400, 3,720,228, and 3,817,277 restraining straps trap the ends of the flapper pin in the flapper pin groove to keep the pin in place. In U.S. Pat. No. 4,274,436 the pipe flange traps the upper horizontal section of the flapper pin in the flapper pin groove.
In U.S. Pat. No. 3,933,173 (and U.K. No. 1,214,619) the flapper pin is trapped in its groove in the valve supporter because the inner face of the valve supporter (which face contains the groove) abuts the face of the counterbore in which the valve supporter is located (see, e.g., FIGS. 1-3). In FIGS. 7-8 of U.S. Pat. No. 4,230,150 a valve is shown in which the flapper pin is trapped in a groove that is closed by a mating surface of the valve. Finally, a retainer to hold a flapper pin in a groove is shown in U.S. Pat. No. 4,201,241.
Despite the foregoing, there is a continuing need for simple, reliable, relatively inexpensive check valves.